In Long Term Evolution (LTE) defined in 3rd Generation Partnership Project (3GPP), as one of access restriction mechanisms for restricting access from a User Equipment (UE) to an access network (IP-CAN), Service Specific Access Control (SSAC) restricting a specific communication service (e.g., voice communication or video communication) is defined (for example, Non-patent documents 1 and 2). Specifically, in activating a function of IMS Voice (MMTEL-Voice) or IMS Video (MMTEL-Video) both involving IP multimedia subsystem (IMS), a UE determines whether access to the IP-CAN is allowed or not based on broadcast information (System Information Block (SIB)) broadcasted from the IP-CAN, and determines whether or not to request origination of a call via the IP-CAN.
FIG. 1 shows a sequence of how SSAC is implemented between a User Equipment (UE) in an RRC IDLE state and an access network (IP-CAN). As shown in FIG. 1, once SSAC is started, the IP-CAN sends broadcast information containing SSAC related parameters to the UE (S10). The broadcast information informs of the start of SSAC and a service to be restricted. The UE retains the SSAC related parameters broadcasted thereto (S20).
Thereafter, based on user's operation or the like, the UE requests to originate voice communication (IMS Voice) or video communication (IMS Video) via the IMS (S30). Specifically, the UE requests the call origination while in the RRC_IDLE state in which connection to the IP-CAN is not established on a radio resource control (RRC) layer. The UE compares the SSAC related parameters retained by the UE with an access class of the UE (e.g., 11 to 15), and determines whether access to the IP-CAN for the call origination is allowed or not (S40). The UE determines whether or not to access the IP-CAN by comparing the parameters notified of through the broadcast information with a random number generated within the UE. If determining that access is allowed, the UE performs processing for originating IMS Voice or IMS Video.
If determining that access is allowed, the UE sends the IP-CAN a RRC Connection Request to request connection to the IP-CAN on the RRC layer (S50). Upon receipt of the RRC Connection Request, the IP-CAN sends the UE an RRC Connection Setup permitting the call origination (S60). After the establishment of RRC Connection, processing for security authentication, Non Access Stratus (NAS) signaling (Service Request), and the like are performed, and the voice communication or video communication via the IMS is started (S70). On the other hand, if determining that access is not allowed, the UE cancels the call-origination request (S80), and activates a timer for measuring a period of time for which origination of INS Voice or IMS Video is barred (S90).
FIG. 2 shows a sequence of how SSAC is implemented between a User Equipment in an RRC CONNECTED state and an access network. As shown in FIG. 2, after SSAC is started, the UE performs packet communication or the like and transitions to the RRC CONNECTED state (S35). In the RRC CONNECTED state, the UE interprets “restricted” in the SSAC related parameters as “not restricted” (S45). By such operation, the UE in the RRC CONNECTED state is excluded from targets of the access restriction according to SSAC.
Thereafter, in the same manner as the case where the UE is in the RRC IDLE state, the UE requests to originate voice communication (INS Voice) or video communication (INS Video) via the INS based on user's operation, and determines whether access to the IP-CAN for the call origination is allowed or not (S45, S55, S65).
If determining that access is allowed, the UE sends the IP-CAN a call-origination request message (SIP_INVITE) according to Session Initiation Protocol (SIP) (S75). The IP-CAN sends the UE a response (SIP_200 OK) to this message received (S85). As a result, voice communication or video communication via the IMS is started (S95).